1. Field of the Invention
The invention relates to an apparatus for melting and refining glass from vitrifiable materials, more commonly called a melting furnace, with a view to the continuous supply of molten glass to forming installations, either for flat glass such as in rolling or float installations, or for hollow glass such as a plurality of forming machines.
The invention is more particularly directed at melting furnaces for flat glass with high molten glass production capacity levels which can, e.g., represent melting rates or outputs of at least 10 tonnes/day and can even reach 1000 and more tonnes/day. However, it is also advantageous for smaller furnaces.
2. Background of the Related Art
In known manner, such a furnace is generally broken down into a succession of compartments issuing into one another and each having specific functions and dimensions. The furnace must be able to melt vitrifiable materials and guarantee the chemical and thermal homogeneity of the glass when malted.
EP-B-264 327 discloses a melting furnace structure having a first compartment in which melting and refining of the glass-making composition takes place, followed by a second compartment forming a neck. The neck issues into a compartment in which thermal homogenization of the molten glass takes place and which is known as a conditioner. The conditioner issues into a flow channel having a significantly reduced section size, which discharges the molten glass to a forming installation.
Furnaces can be placed in two major categories as a function of the heating means used for melting the vitrifiable materials in the melting compartment.
On the one hand there are electric melting furnaces of the so-called cold top type, such as is e.g. known from EP-B-304 371, where melting taken place by electrodes immersed in the depth of the molten glass.
There are also fired furnaces, also known as regenerative furnaces, such as are known from U.S. Pat. No. 4,599,100. In this case, the heating power is supplied by two rows of burners generally operating with a fuel-air mixture and arranged in alternating manner. The combustion gases then alternately heat one or other of two regenerators positioned in facing manner on either side of the melting compartment and communicating therewith. The combustion gases are thermally extracted through stacks of refractories, which constitute the regenerators and which then restore the heat to the melting compartment.
This heating method is effective and widely used. But it suffers from a certain number of disadvantages inherent therein. For example, the energy costs of the fuel-air burners are relatively high. Moreover, the operating system of the burners, which are activated in an alternating manner with cycles of approximately 20 to 30 minutes, is not easy to strictly control. Their use also leads to the introduction into the melting compartment of a significant quantity of air and therefore nitrogen, which leads to an increased risk of forming polluting gases of the NO.sub.x type, which must then be treated.
Finally, the large amount of special, costly refractories necessary for the manufacture of the regenerators significantly increases the furnace construction costs.